Relays


A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called “protective relays”.

Magnetic latching relays require one pulse of coil power to move their contacts in one direction, and another, redirected pulse to move them back. Repeated pulses from the same input have no effect. Magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts.

Magnetic latching relays can have either single or dual coils. On a single coil device, the relay will operate in one direction when power is applied with one polarity, and will reset when the polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands.

source: Wikipedia – Relays

ahm.. words and terminology are too deep right? alright. Lets focus on… lets say famous or always used relays in prototyping and explain it more simpler .

Electromechanical Relays

These are the ones you can always see on electronics or robotics stores like ours. This type of relay has an Electromagnetic coil – an enamel coated copper wrapped around a core – that generates an electromagnetic field that attracts or pulls any nearby metal objects. In our case, it pulls something called an Armature. An Armature is the part that holds the Common (C) contact terminal that is attached to the  spring. The spring pulls the armature back to its resting or de-energized state. The Normally Closed (NC) terminal is where the armature connects to when the relay mechanism is de-energized. Lastly, the Normally Open (NO) terminal is where the armature connects to when the relay mechanism is energized.

In short, relays act like manual switches but can be integrated in automation projects.

How does the whole mechanism work?

Watch this video:

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Where can i use these relays?

ac light bulb

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Microcontroller Controlled DC Fan and AC Light Bulb

All in all, the invention of the relay greatly helped to improve the automation industry. It is a tremendously useful yet simple mechanism that almost 70% of devices use it today!

I hope you learned something from my post!

-bok pogi